Browser extension nightly DOM checks
Created by: eseliger
This works on #7980 (closed) I added a new pipeline to Buildkite that runs on a schedule (every day at midnight) and failures are posted to #web, so we get notified. After we finally managed to fix the tests, this tests for DOM changes on github.com and gitlab.com (browser extension, not native integration). For an example run see here: https://buildkite.com/sourcegraph/browser-extension-nightly/builds/1
TODO after merge: Need to set the target branch for the scheduled build to master